There are many types of bottles for feeding nursing infants through a flexible nipple. If excessive vacuum accumulates in the bottle, it can be hard for the infant to draw fluid through the nipple. Some bottles have internal pouches that collapse as they are emptied. Others have various types of venting systems that allow air to enter the bottle during feeding. However, air ingestion can be a source of discomfort for infants. It is also desirable that bottle venting systems not excessively leak.
Improvements are continually sought in the design of venting systems for bottles.